Increased levels of nitrate and other nutrients in ground water have been documented in hundreds of locations throughout the United States. According to published reports, individual, on-site septic systems are a primary non-point source responsible for increased nitrate levels. Individual on-site septic systems in fractured bedrock aquifers are especially susceptible to elevated nutrient levels, as bedrock soils have limited ability to filter drainfield effluent. Also, recent studies have shown widespread evidence of pharmaceuticals and personal care products (PPCPs) in water resources. As populations tend to expand away from urban centers and toward the outer reaches of valley floors, the issue of elevated nutrient concentrations will become more important.
Nitrogen is present in many forms in a septic system. Most nitrogen excreted by humans is in the form of organic nitrogen (dead cell material, proteins, and amino acids) and urea. After entering the septic tank, microorganisms convert organic nitrogen to ammonia. Ammonia is the primary form of nitrogen leaving a standard septic system. Biological conversion of ammonia to nitrogen gas is a two-step process. Ammonia must first be oxidized to nitrate; nitrate is then reduced to nitrogen gas. These two reactions require significantly different environments.
Conversion of ammonia to nitrite and then to nitrate, is called nitrification. It is important to note that nitrification requires and consumes oxygen. The process is mediated by the bacteria Nitrosomonas and Nitrobacter, which require an aerobic environment for growth and metabolism of nitrogen. In a conventional septic system, most ammonia is converted to nitrate beneath the drainfield, where no further treatment occurs. As a result, nitrate is the primary contaminant of concern from on-site septic systems. As urban sprawl and rural development continues, domestic wells and surface water bodies are increasingly being impacted by nitrate from multiple septic system effluent.
The second step of the process, the conversion of nitrate to nitrogen gas, is referred to as de-nitrification. This process is also mediated by bacteria. For de-nitrification to occur, the dissolved oxygen level must be at or near zero. The bacteria also require a carbon food source for energy and conversion of nitrogen. The bacteria metabolize the carbonaceous material or biological oxygen demand (BOD) in the wastewater as this food source, metabolizing it to carbon dioxide. This in turn reduces the BOD of the sewage, which is desirable. However, if the sewage is already low in BOD, as is the case in the nitrification/de-nitrification process, the carbon food source will be insufficient for bacterial growth and de-nitrification will not proceed efficiently.
Nitrate can have serious human health effects if consumed in drinking water. Nitrate, other forms of nitrogen and phosphorus can have deleterious effects on the environment, as excess nitrogen stimulates the process known as eutrophication in surface water bodies. For this reason, many alternative technologies have been designed to remove total nitrogen from wastewater. See, for example, U.S. Pat. Nos. 7,485,228 B2; 7,462,285 B2; 7,445,715 B2; 7,407,580 B2; 7,332,077 B2; 7,297,276 B2; 7,147,776 B2; 7,144,509 B2; 7,082,893 B2; 7,081,203 B2; 7,077,952 B2 6,946,074 B2; 7,008,538 B2; 6,946,073 B2; 6,936,170 B2; 6,818,581 B2; 6,582,596 B2; 6,444,126 B1; 6,372,137 B1; 6,187,183 B1; 5,342,522; and 5,318,699 and U.S. Published Patent Application Nos. 2008/0210610 A1; and 2008/0156726 A1. See also, JP 54,107,153; and WO 1988/003515 as well as HU et al, Treatment of Wastewater with Modified Sequencing Batch Biofilm Reactor Technology, J. or Shanghai University, 2002, 6(3): 248-254. These technologies use bacteria to convert ammonia and nitrate to gaseous nitrogen. In this form, nitrogen is inert and may be released to the air. Most existing systems use inefficient trickling filters or have little active aeration and accomplish only about 70% to 80% nitrification.
Although systems have been developed to remove total nitrogen from wastewater. These systems are often difficult to administer and monitor, are intricate and complicated to install, and are inefficient. A need therefore remains for a simple system that effectively removes total nitrogen from wastewater.
All patents, patent applications, provisional patent applications and publications referred to or cited herein, are incorporated by reference in their entirety to the extent they are not inconsistent with the teachings of the specification.